Method and apparatus for riveting with titanium alloys

ABSTRACT

A device for cold forming a titanium alloy rivet according to a precise force vs. time relationship selected to avoid work hardening of the rivet. An electrical control circuit produces a squeeze signal waveform corresponding to the desired force rate variations to be exerted on the rivet. The squeeze signal operates a fluid pressure regulator on a hydraulic pump to control the force exerted on the rivet by opposed hydraulic squeeze cylinders. The electrical control circuit also produces switching signals for operating directional flow control valves in a hydraulic control circuit for moving the squeeze cylinders into and out of engagement with the rivet. Hydraulic clamp cylinders are used to hold the articles being riveted and the electrical control circuit produces signals for controlling the force exerted by the clamp cylinders and for moving the clamp cylinders into and out of engagement with the articles. The hydraulic control circuit associated with the clamp cylinders also includes means for floating the cylinders.

United States Patent Inventors Charles Newman 11653 Southeast 49th, Bellevue, Wash. 98004; B. James Clement, 1042 S. 173rd, Seattle, Wash. 98148 [211 App]. No. 819,033 [22] Filed Apr. 24, 1959 [45] Patented Sept. 7, 1971 [54] METHOD AND APPARATUS FOR RIVETING WITH TITANIUM ALLOYS 20Claims, 7 Drawing Figs.

[52] U.S. Cl 72/28, 7 72/305, 72/407, 72/453 [51] Int. Cl ..-B21j 15/02 [50] Field of Search 72/453, 407, 28, 295, 296, 297, 305

[56] References Cited UNITED STATES PATENTS 586,197 7/I897 Morgan 72/430 1,010,938 l2/l9ll Merkl..... 72/430 1,232,050 7/1917 Kraemer. 72/407 3,209,577 10/1965 Teplow 3,274,819 9/1966 Knowles...

Primary Examiner-Charles W. Lanham Assistant Examiner-Gene P. Crosby ABSTRACT: A device for cold forming a titanium alloy rivet according to a precise force vs. time relationship selected to avoid work hardening of the rivet. An electrical control circuit produces a squeeze signal waveform corresponding to the desired force rate variations tobe exerted on the rivet. The

squeeze signal operates a fluid pressure regulator on a hydraulic pump to control the force exerted on the rivet by opposed hydraulic squeeze cylinders. The electrical control circuit also produces switching signals for operating directional flow control valves in a hydraulic control circuit for moving the squeeze cylinders into and out of engagement with the rivet.

67- I84]? IXEf JTH- I79 w. I 5! 5/ 55 -57 mo /OI PATENTEU SEP 7 I97! SHEET 1 BF 3 INVENTORJ. CHARLES W. NEWMA WIAMES CLEMENT PATENTEDSEP H971 SHEET 2 [1F 3 3 *K YE 2 A -4 1 2 57 SQUEEZE PRESSURE 34 4o BOTH 015s 2? 50 3/ TOP DIE Ld, W BOTTOM r; 55 DIE 3g 4/.

3? CLAMP 5 N 9 PRESSURE 59 BOTH CLAN/L 7 13 TOP CLAMP 7 9 TIME BOTTOM r- P 4.2 I! CLAMP 4.2

Isa Hg Z 8 "I46 QUARTER -v COUNT E1 POWER GATE INPUT 4 I25 I29 K? (12% I50 [28 [3P 1 cumnvr couwrm M R5347 I 3 44 J Zogmmm L C 1 I I wNmoL I42 4 I49 I 6 3 iii PANEL I24 I, 5.7 up

' I 7 T 14a PUMP 7 I2! VARIABLE MANUAL m c0 RATE w m COUNT 056. l L TE INVENTORS, CHARLES W NEWMAN q J'AMES CLEMENT METHOD AND APPARATUS FOR RIVETIN G WITH TITANIUM ALLOYS BACKGROUND OF THE INVENTION The present invention relates generally to methods and apparatus for controlling the force exerted on a workpiece by a tool such as a pressure cutting or pressure forming tool. Specifically, the present invention relates to methods and apparatus for cold-forming titanium alloys thereby enabling an unheated titanium alloy rivet to be compressed between the dies of a riveting machine without work hardening the alloy.

As is the case with many materials, the energy generated within the material during compression gives rise to chemical reactions, crystalline structural changes and other internal changes which weaken the material or otherwise adversely affect a particular characteristic that renders it unsuited for the job for which it was intended. In the case of a titanium alloy, compression forces can cause changes in its crystalline structure rendering the alloy brittle in which case it is said to have been work hardened." These internal changes within a material can be avoided or at least minimized by closely controlling the magnitude and rate of application of the compression force. In this regard, prior art control mechanisms have proven unsatisfactory in failing to provide exact control over the compression force exerted on a workpiece.

The control mechanism commonly available for use with pressure-forming machines control the maximum force level or the final shape of a workpiece. Some machines provide continuous force control but normally are responsive to the movement of the tool or the workpiece. These controls are unsatisfactory when either the increments or rates of tool movement are too small for accurate measurement or for effecting a significant machine response. Riveting machines, for example, characteristically employ short stroke, rapid tool movement work cycles and the control mechanisms normally employed with them merely limit the maximum force applied to the rivet. These control mechanisms are particularly inadequate for compressing titanium alloy rivets.

Accordingly, it is an object of the present invention to improve methods and apparatus for cold working titanium alloy rivets. In particular, it is an object to compress materials under closely controlled, predetermined forces to prevent or minimize undesirable changes in the structural characteristics of the material. In the present invention a titanium alloy rivet is gripped between opposed tools and squeezed according to a generally increasing force curve to a maximum force level and thereafter the force is reduced to a lower level before the rivet is released from the grip of the tools. In the presently preferred embodiment of the invention the increasing force is developed along linear force curves of successively decreasing slope, i.e. generally exponentially. However, the present invention is not limited to the working of titanium alloys or even to the operation of riveting machines because it is capable of producing force variations other than the foregoing in order to suit the requirements of other pressure-exerting operations. It is therefore another object of the invention to provide in pressure-exerting machines, means for varying the force exerted on a workpiece according to prescribed force variations required by a particular pressure-exerting operation.

In the present invention, a hydraulic squeeze circuit controls the movement and'force of a tool by controlling the direction of fluid flow and fluid pressure delivered to hydraulic squeeze cylinders to which the tools are attached. An elecrrical command circuit generates electrical signals which operate directional flow control valves and which regulate the fluid pressure in the hydraulic cylinders. The signals effecting pressure changes have wave shapes corresponding to the desired force variations to be applied to the workpiece. It is accordingly another object of the present invention to device electrical signal generators for producing signal waveforms corresponding to desired force variations. It is also an object to devise means for generating electrical switching signals to effect changes in the direction of fluid flow in the hydraulic circuit. Another object in keeping with the foregoing is to devise a hydraulic circuit capable of effecting fluid pressure variations and fluid-flow direction changes in response to the aforementioned electrical signals to obtain a desired movement and force application for the tool.

In the case of a riveting machine, a separate hydraulic circuit is employed in conjunction with the electrical and hydraulic squeeze circuit to control the movement and force exerted by hydraulic clamp cylinders used to restrain the lateral movement of the articles being riveted. The clamp cylinders grip I and hold the articles and exert a generally constant force on the articles during the riveting operation. The clamp cylinders are automatically floated" when a rivet is sufficiently expanded to lock the articles together. Top and bottom clamp cylinders grip the articles and are floated when the bottom cylinders follow the movement of the top cylinders while continuing to maintain their grip on the articles. Accordingly it is still another object of the present invention to devise improved methods and apparatus for gripping and holding articles being riveted.

The clamp and squeeze cylinders of the present invention are double acting cylinders and the hydraulic control circuits are capable of delivering fluid to one or both sides of the pistons within the cylinders in order to obtain different force levels for a given fluid pressure level. Another object of the present invention is therefore to incorporate in an electrically controlled fluid-operated circuit a multiple force range capability.

DESCRIPTION OF THE DRAWINGS Other objects and features of the invention will be apparent from a further reading of the description of the invention in conjunction with the drawings which are:

FIG. 1 is a functional schematic diagram of the fluidoperated control circuit for the clamp and squeeze cylinders;

FIG. 2a and 2b illustrate the fluid pressure waveforms resulting from the electrical signal waveforms utilized to control the hydraulic circuits in the present invention;

FIG. 3 is a functional schematic of the electrical command circuit for controlling fluid pressure in the squeeze cylinders;

FIG. 4 is a simplified functional schematic of the electrical circuit and associated switching relays for controlling fluid pressure in the clamp cylinders;

FIG. 5 is a simplified functional schematic of the relay switching logic for operating the directional flow control valves associated with the clamp cylinders; and

FIG. 6 is a simplified functional schematic of the relay switching logic for operating the directional flow control valves associated with the squeeze cylinders.

DESCRIPTION OF THE INVENTION The waveforms shown in FIGS. 2a and 2b are graphical plots of pressure vs time. The waveforms shown represent an example of the magnitude and duration of the pressures used to clamp and hold the articles being riveted and for squeezing a titanium alloy rivet. The force variations are obtained by varying the fluid pressure in fluid-operated cylinders which clamp the articles and squeeze the rivet. These fluid pressure variations are obtained by generating electrical signals which operate pressure control devices. Squeeze curve 1 represents the pressure exerted to squeeze the rivet and clamp curve 5 represents the pressure exerted to clamp the articles. Squeeze curve 1 includes the two ramp portions 2 and 3, which are linearly increasing curves of decreasing slope, and the exponentially decaying portion 4. Experiments have shown that work hardening" of titanium alloy rivets is substantially eliminated by increasing the force exerted on the rivet at a closely controlled decreasing rate of change of force. Accordingly, satisfactory results have been obtained using the force-time relationship that results from the pressures indicated by curve I. The amplitude or magnitude of the force is dependent upon the physical characteristics of the rivet such as its size and particular composition of materials. The duration of the force is similarly dependent on the physical characteristics of the rivet but is generally in a range of /2l0 seconds, at least for the ramp portion 2 and 3, for a wide variety of rivet sizes.

Clamp curve 5 includes the rise portion 7, the constant level portion 8 and the decay portion 9. As with the squeeze force, the clamp force must be at least sufficient to hold the articles during the riveting operation and in the present embodiment is held at the constant level resulting from the pressure indicated 7 by pressure level 8 until the squeeze force has been reduced to a safe level. Definite rise and fall times (portions '7 and 9) are provided for curve 5 to minimize the occurrence of transient forces (i.e. shock) in the system.

The work cycle of the riveting operation is illustrated by the curves. First the articles are engaged by the clamp cylinders represented schematically in FIG. 1 by the top clamp cylinders 14 and bottom clamp cylinders 15. One top and one bottom clamp cylinder are positioned on either side of the squeeze cylinders to grip and hold the articles during the riveting operation. Curve [0 (FIG. 2) represents the fluid pressure in the bottom clamp cylinders for advancing the bottom clamp die into engagement with the articles and curve 11 represents a similar pressure level in the top clamp cylinders. Curve 12, which extends below the reference line 13, represents a pressure level for retracting the top clamp cylinders to allow realignment of the clamp dies with the articles. This initial engagement of the articles is controlled manually. Next, the rivet is inserted into a hole or cavity in the articles during the time interval 13a and a start clamp command signal is issued to automatically pressurize the top and bottom clamp cylinders to the constant force level 8.

After the articles are gripped by the clamp cylinders, the rivet is engaged between the top and bottom squeeze cylinders 27 and 28 represented schematically in FIG. 1. Curves 29 and 30 (FIG. 2a) represent a manually controlled extension and retraction of the top squeeze cylinder to obtain an initial alignment with the rivet. Thereafter, the squeeze operation is under automatic control initiated by a manual pushbutton signal. The fluid pressure in the top squeeze cylinder is sufficient to extend its piston rod but the pressure is initially limited to the level of curves 29 and 31-33 by a relief valve momentarily inserted into the fluid control system. Next the fluid is admitted to the bottom squeeze cylinder. Pressure in both squeeze cylinders is limited to the level of curves 31-33. This initial limiting of the squeeze force minimizes the occurrence of transient forces. After the limiting relief valve is switched out of the system, the fluid pressure in the top and bottom squeeze cylinders is increased according to the ramp portion 2-of the squeeze curve 1. When the fluid pressure in the squeeze cylinders reaches point 34, the clamp cylinders are floated." The clamp cylinders are said to be floating" when the bottom clamp cylinders are free to move up and down without releasing their grip on the articles. This operation will be explained later in connection with the description of the clamp cylinders fluid control circuit. At point 34 on curve 1, a rivet is sufficiently expanded to fill the hole in which it is inserted thereby locking the articles together. Point 34 occurs generally at a force level that is 25 percent of the maximum force exerted on the rivet. I

When the fluid pressure in the squeeze cylinders reaches brealtover point 35 the pressure is increased at the slower rate of ramp 3 up to the maximum force level 36. The pressure is held at the maximum level 36 for a short period 36a to permit u readout device to record and/or display the force exerted on the rivet. The display is a means to check whether the rivet has undergone the specified compression.

Following time delay 360, the fluid pressure is decreased according to the exponentially decaying curve 4. At the same time interlock and squeeze decompression clocks or timers are started. The interlock timer prevents the clamp cylinders from releasing their grip on the articles until the squeeze pressure is reduced to a safe level, namely point 37 on curve 1. The squeeze decompression timer allows the squeeze pressure to decrease to level 40 on curve 1 at which time the squeeze cylinders disengage the rivet and retract. The curve 41 represents the fluid pressure required to retract the piston rods of the squeeze cylinders. When the piston rods are fully retracted, the fluid pressure builds up as indicated by point 41a on curve 41. A pressure switch senses the buildup of pressure and cuts off the supply of fluid to the squeeze cylinders and initializes the appropriate control devices in the system.

The decompression of the fluid pressure in the clamp cylinders is initiated manually and may occur anytime after the squeeze pressure is reduced to level 37. A clamp decompression timer is initiated when the clamps are to be retracted and the timer allows the pressure to decrease according to portion 9 of the clamp curve 5 until it reaches level 39. At this time the clamp cylinders disengage the articles and retract. The curve 42 represents the fluid pressure required to retract the piston rods of the clamp cylinders and when the piston rods are fully retracted, the fluid pressure builds up as indicated by point 42a on curve 42. A pressure switch senses the buildup of pressure and cuts oh the supply of fluid to the clamp cylinders and initializes the appropriate control devices in the system.

THE HYDRAULIC CONTROL CIRCUITRY The control circuitry and cylinders employed in the presently preferred embodiment of the invention are hydraulic devices but it should be understood that the system could be adapted to employ pneumatic devices. Therefore, the term fluid is used in the description of the invention and is intended to encompass gas-operated as well as liquid-operated apparatus.

The squeeze and clamp cylinders 27, 28, 14 and 15 are double-acting hydraulic cylinders capable of operation with an appropriate hydraulic oil. The cylinders have pistons and piston rods slidable within the cylinders defining extension and retraction chambers within the cylinders on either side of the piston. The piston rod is extended or retracted when fluid is directed to the extension or retraction chamber. The surface areas of the piston on which the fluid acts within the extension and retraction chambers differ by the ratio 4:3 for the squeeze cylinders and 2:1 for the clamp cylinders. Consequently, for a given fluid pressure the cylinders can be operated within two distinct force ranges. A high force range is available when fluid is supplied only to the extension chambers, in which case the force exerted by the piston is proportional to the area on one side of the piston. A lower force is available when fluid is simultaneously supplied to both the extension and retraction chambers wherein the force exerted by the piston is proportional to the difference in surface areas on opposite sides of the piston. For a given pressure, the 4:3 surface area ratio for the squeeze cylinders provides a high force range for them four times as great as the low force range and the 2:1 surface area ratio for the clamp cylinders provides a high force range for them twice as great as the low force range.

The extension and retraction of the squeeze and clamp cylinders, i.e. their piston rods, is controlled by the fluidoperated control circuit of FIG. 1. The master control valves 17 and 18, the float control valve 19, the pilot-operated check valve 41-5 and the range valves 46 and 47 control the operation of the clamp cylinders 14- and 15. The master control valves 17 and 18 route fluid to either the extension or retraction chambers of the clamp cylinders, range valves 46 and 47 modify the flow of fluid to operate the cylinder in the high and low force ranges and float control valve 19 and pilot-operated check valve 45 operate in concert to float" the clamp cylinders.

The master control valve 20, auxiliary valve 48, range control valve 49 and pressure limit valve 54 control the operation of the squeeze cylinders 27 and 28. The master valve 20 routes fluid to the extension chamber of cylinder 27 and to the retraction chambers of both the cylinders 27 and 28, auxiliary valve 48 routes fluid to the extension chamber of cylinder 28, range control valve 49 modifies the fluid flow to operate the cylinders in the high and low force ranges and pressure limit valve 54 switches the relief valve 103 into and out of the circuitry during initial engagement of a rivet.

Valves l7, 18, 19 and 20 are solenoid controlled, spring centered, four-way spool valves, valves 46,47 and 49 are solenoid controlled, spring biased, two-way spool valves and valves 48 and 54 are solenoid controlled, spring biased, three way spool valves. The schematic representations of these valves include blocks which indicate the paths through them at their various valve positions. In FIG. 1, all the valves are shown coupled to the fluid conduits at their spring biased or spring centered valve positions. The valves 17-20 have three valve positions indicated by the right, left and center blocks of their schematic representations. The valves shift to their left valve positions when their left solenoids 17c, 18d, 19a and 20v are energized and they shift to their right valve positions when their right solenoids 17g, 18h, 19b and 20y are energized. The valves are at their center valve positions when neither their left or right solenoids are energized. The valves 46, 47, 48, 49 and 54 have two valve positions indicated by the right and left blocks of their schematic representations. The valves are at their left valve position when their solenoids 46e, 47f, 48w, 49x and 542, are not energized and shift to their right valve position when these solenoids are energized.

A fluid supply for the system is stored in reservoir 51 and is pumped from the reservoir by variable displacement pump 50 and by constant displacement pump 52. The variable displacement pump supplies pressurized fluid to the squeeze cylinders 27 and 28 and the constant displacement pump supplies pressurized fluid to the clamp cylinders 14 and 15.

Turning now to the clamp circuit, constant displacement pump 52 delivers fluid to the clamp master control valves 17 and 18 via conduits 55, 56 and 57. Initially the valves 17, 18 and 19 are at their center valve positions with valves 17 and 18 blocking the flow of fluid to the clamp cylinders and valve 19 venting the fluid from pump 52 back to the reservoir 51 thereby preventing unnecessary power consumption by motor 53 when the clamp cylinders are not in use. The clamp cylinders are extended into engagement with the articles being riveted when valves 17, 18 and 19 are switched to their left valve positions. Valve 19 seals off conduit 55 and valves 17 and 18 pass the fluid to the extension chambers of the cylinders. Fluid flows to the top clamp cylinders 14 via conduit 60 and check valve 66a. As the cylinder extends, fluid in the retraction chambers of cylinders 14 is vented to reservoir 51 via conduit 62, check valve 660, range valve 46, conduit 63 and master valve 17.

Range valve 46 is switched to its right valve position to select the low force range capability of the top clamp cylinder. At this valve position, the fluid flowing to the extension chambers in conduit 60 is simultaneously routed to the retraction chamber through conduit 64, range valve 46, check valve 66d and conduit 62.

To retract the top clamp cylinders, master valve 17 is switched to its right valve position and range valve 46 is switched to its left valve position if the low force range is being employed. Fluid from the pump 52 flows to the retraction chambers via conduit 63, range valve 46, check valve 66d and conduit 62. The fluid in the expansion chamber is vented to reservoir 5] via check valve 66b, conduit 60 and valve 17.

Master valve 18 functions in a similar manner to valve 17 to extend and retract the bottom clamp cylinders 15. When valve 18 is at its left valve position fluid flows through it to the extension chambers of the cylinders 15 via conduit 67, pilotoperated check valve 45, check valve 66e and conduit 68. The fluid in the retraction chambers of cylinders 15 is vented to reservoir 51 via conduit 69, range valve 47 (at is left valve position) conduit 70 and valve 18.

Range valve 47 is switched to its right valve position to select the low force range capability for cylinders 15. At this valve position, the fluid flowing to the extension chambers in conduits 67-68 is simultaneously routed to the retraction chambers through conduit 71, range valve 47, and conduit 69.

To retract the bottom clamp cylinders 15, master valve 18 is switched to its right valve position, range valve 47 is switched to its left valve position if the low force range is being employed and float control valve 19 is switched to it right valve position. Fluid flows from pump 52 to the retraction chambers via conduit 70, range valve 47 (left valve position) and conduit 69. The fluid in the expansion chambers is vented to reservoir 51 via conduit 68, check valve 66f, pilot operated check valve and conduit 67. Pilot check valve 45 is opened to permit free flow in either direction when float control valve 19 is at its right valve position. Valve 19 applies the pressurized fluid in conduit to the pilot operator of valve 45 through conduit 76 to open the check valve 45.

Float control valve 19 is normally switched to its right valve position before the bottom clamp cylinders 15 are retracted in order to float the cylinders. Prior to opening pilot operated valve 45, fluid in the extension chambers of the bottom cylinders 15 cannot be vented because valve 45 allows fluid to flow in only the direction toward cylinders 15 at this time. Therefore, any net force downward on the bottom cylinders will not cause these cylinders to move although the fluid pressure will increase. Relief valve 75 vents fluid to reservoir 51 in the event excessive pressures occur in the extension chamber of cylinder 15. However, when valve 45 is opened, i.e. made free flowing in either direction by the application of a pilot pressure to it through valve 19, the conduits supplying fluid to the extension chambers of both the top and bottom cylinders 14 and 15 are tied together by virtue of the conduit 55 connected to the pump 52. Consequently, any net upward or downward force exerted on the articles being riveted will cause the clamp cylinders to move with the force without releasing their grip on the articles by routing fluid displaced from one set of cylinders to the other. The floating operation is substantially the same when the range valves 46 and 47 are in their right valve positions since the input lines and 67 to the extension chambers are still in fluid communication with each other when pilot operated check valve 45 is open.

Spring biased check valves 66a in the clamp circuit and 661' in the squeeze circuit create an unbalance of forces in their respective circuits. The total piston area of cylinders 14 is substantially equal to the total piston area of cylinders 15 and a net upward or downward force would normally not be exerted on the articles by the clamp cylinders. However, the spring bias on check valve 66a lowers the fluid pressure in the exten sion chambers of top clamp cylinders 14 relative to the fluid pressure in the extension chambers of cylinders 15 thereby giving rise to a small but net upward force. The piston areas of squeeze cylinders 27 and 28 are also substantially equal to each other. Consequently, the spring bias on check valve 66i lowers the fluid pressure in the extension chamber of the bottom squeeze cylinder 28 relative to the top squeeze cylinder 27 thereby giving rise to a small but net downward force. Prior to floating" the clamp cylinders, any unbalance in these forces does not cause the rivet to move relative to the articles because the clamp cylinders are locked against downward movement by the pilot operated check valve 45 and the tool coupled to the top squeeze cylinder includes means for bearing against the articles as well as the rivet thereby preventing any upward movement. As a result, the rivet remains in the cavity within the articles prior to floating the cylinders. When the rivet is sufficiently expanded to lock it to the articles the cylinders are floated" by opening valve 45. The clamp cylinders are floated" when they are not locked against movement because their input lines to their extension chambers are completely in fluid communication with each other. As mentioned earlier, the rivet is sufficiently expanded to fill the cavity in the articles at approximately 25 percent of the maximum force applied to the rivet. The cylinders are floated when the squeeze force reaches the 25 percent level and the articles are free to move as a result of any unbalance of the forces acting on them.

Spring-biased check valves 66c and 66fin the clamp circuit and 66h in the squeeze circuit are used to counterbalance the weight of the piston rods and the tools attached to them by creating forces that act against their weight.

Check valves and associated orifices 79 and 80 are coupled by conduits 81, 82 and 83 to the top and bottom extension chamber conduits 60 and 67. Valves 79 and 80 isolate conduits 60 and 67 from each other and provide, along with solenoid controlled relief valve 84, means for controlling the fluid pressure in the top and bottom clamp cylinders. Conduit 85 couples relief valve 84 to reservoir 51 and isolation conduit 82. The force exerted by the control solenoid on valve 84 establishes the pressure level in the clamp cylinders. Therefore varying the electrical signals energizing the solenoid on valve 84 causes a proportional variation in the fluid pressure in the clamp cylinders. The solenoid on valve 84 is controlled by an electrical signal corresponding to curve in FIG. 2b to effect corresponding pressure variations for the clamp cylinders.

Likewise, check valves and associated orifices 90 and 91 are coupled between the retraction chamber conduits 63 and 70 by conduits 92, 93 and 94. Valves 90 and 91 isolate the conduits 63 and 70 and provide means, along with pressure switch 95, for monitoring pressure in the retraction chambers of the clamp cylinders. Pressure switch 95 is coupled to conduit 93 by conduit 96 and is activated by the pressure increase 42a shown in FIG. 2 that occurs when cylinders 14 and complete their retraction. Switch 95 is normally closed and the opening of its contacts caused by this pressure increase acts to initialize the clamp system.

Accumulator 99 is a device for preventing momentary loss of line pressure when float control valve 19 is switched between its various valve positions. Valve 19 is switched from its left position to its right position when the clamp float occurs. The accumulator is charged with a gas which maintains the pressure in conduit 55 during the switching of the valve.

Relief valve 275 and 375 afford protection against accidental clamp system overload pressures and are not normally operative.

Turning now to the squeeze circuit, variable displacement pump 50 supplies pressurized fluid to the master valve via conduit 100. Pump 50 hasa solenoid which varies the output pressure of the pump in response to a varying electrical signal. An electrical squeeze command signal corresponding to curve 1 in FIG. 2a is generated by the electrical control circuit and is applied to the solenoid on pump 50 to obtain corresponding pressure variations. The relief valve 101 is coupled to conduit 100 to require the pump 50 to operate above a minimum pressure level. The fluid in conduit 100 is vented to reservoir 51 when valve '20 is at its center valve position to prevent unnecessary power consumption by motor 53 when the squeeze cylinders are not in use.

The squeeze cylinders are extended when master valve 20 is at its left valve position. In this valve position, fluid flows via conduit 102 to the extension chamber of cylinder 27 and to the extension chamber of cylinder 28 if auxiliary valve 48 is at its right valve position via conduits 102 and 104, valve 48, check valve 661' and conduit 112 The retraction chambers for I the cylinders 27 and 28 share a common path for exhaustion of fluid that includes conduit 111, range valve 49 (at its left valve position) and conduit 108. The conduits 109 and 106 couple the retraction chambers of the two cylinders to conduit 111.

Pressure limit valve 54 is coupled to the input conduit 102 feeding the extension chambers and selectively couples or removes relief valve 103 from conduit 102. Relief valve 103 is used to limit the fluid pressure in the extension chambers during initial engagement of the rivet. The switching of valve 103 in and out of the squeeze circuit is described in connection with the electrical control circuitry.

Range valve 49, at its right valve position, routes fluid to the conduit 102 (feeding the extension chambers) from the retraction chambers of cylinders 27 and 28 to operate the switched to its right valve position, range valve 49 is switched to its left valve position if the low force range is being employed, and auxiliary valve 48 is switched to its left valve position. The fluid from pump 50 flows to the retraction chambers via conduit 108, range valve 49, conduit 111 and conduits 109 and 106. The fluid in the extension chambers is vented to reservoir 51 from cylinder 27 via conduit 102 and from cylinder 28 via conduit 112, check valve 66j and auxiliary valve 48 (left valve position). Valve 48 could also be at its right valve position during retraction but is not in order to simplify the electrical circuit as will be made apparent later.

Pressure switch 118 is coupled to the common line or conduit 111 feeding the retraction chambers of the two squeeze cylinders. Switch 118 is activated by the increase in fluid pressure occurring when the squeeze cylinders are fully retracted as indicated by level 41a in FIG. 2a. Electrical contacts on switch 118 deenergize the squeeze circuit solenoids to reduce the fluid pressure to zero and ready the system for subsequent squeeze operations.

Relief valve 475 affords protection against accidental squeeze system overload pressures and is not normally operative.

ELECTRICAL CONTROL CIRCUIT Referring to FIG. 3, the manually operated buttons or switches and system relays which are used to generate the switching command signals that operate the solenoids on the various valves in the fluid-operated circuit are contained within the relay logic control panel 121. Simplified functional schematics of the relay logic 121 are shown in FIGS. 4, 5 and 6. The remainder of the circuit in FIG. 3 is used to generate the electrical squeeze command signal corresponding to curve 1 (FIG. 2a) and to apply the squeeze signal to the control solenoid on variable displacement pump 50 to effect a like variation in fluid pressure in the squeeze cylinders. Coil 122 represents the control solenoid of pump 50.

The curves in FIGS. 2a and b define the work cycles of the clamp and squeeze cylinders. The ramp portions 2 and 3 of curve 1 define the squeeze cycle for the squeeze cylinders and the decaying portion '4 defines their decompression cycle. The ramp signals 2 and 3 are generated by the squeeze cycle generator which includes the oscillator 124, the digital counter 125, the digital-to-analog converter (DAC) 126 and the operational amplifier 128. The operational amplifier 128 and capacitor 129 comprise the decompression cycle generator while current control circuit 130 is an output circuit which produces a power signal compatible with the control solenoid on pump 50, i.e. coil 7122. A variable displacement pump with electrically controlled pressure compensator, model number PVHTNHO0SKR, manufactured by the Racine Hydraulics .Corporation, Galena, Ohio is the pump presently preferred for serving the function of pump 50. A Racine Corporation current controller, model CCM8I, is the circuit presently preferred for serving the function of circuit 130. The current control circuit 130 produces an output current for coil 122 which is proportional to the amplitude of the voltage at the output of amplifier 128.

The work cycle of the squeeze cylinders is initiated by closing the start switch 123 in FIG. 6 thereby energizing solenoids 20v and 54z. Master valve 20 is switched to its left valve position to cause the extension of the top squeeze cylinder. Valve 54 is switched to its right valve position coupling the relief valve 103 to the squeeze cylinder input line 102 thereby limiting the pressure buildup in the cylinder 27 to a level corresponding to the level ofcurve 31 in FIG. 20. Start switch 123 also energizes time-delay relay 131 (the auxiliary timer) whose normally open contacts 127 close after a period corresponding to the time period between the beginning of curves 31 and 32 in FIG. 2a. The closing of contacts 127 energizes solenoid 48w on auxiliary valve 48 thereby causing the extension of the bottom squeeze cylinder. The closing of contacts 127 also energizes time-delay relay 132 whose normally closed contacts 119 and 120 open after a time period corresponding to the duration of curve 32 and delay period 33. Opening contacts 119 removes the energizing voltage from solenoid 54;: thereby removing the relief valve 103 from the squeeze circuit. Opening contacts 120 removes the ground potential 116 from the counter 125 and DAC 126. (The counter and DAC are reset to zero when the ground potential 116 is applied to them). Opening contacts 120 initiates the generation of the ramp signal 2 by applying an enabling voltage to AND gate 133 and NAND gate 134, thereby starting the production of ramp portion 2 of curve 1.

Again referring to FIG. 3, NAND gates 134 and 135 are cross-connected to form a direct set flip-flop used to couple either potentiometer 138 or 139 through a diode to the emitter of a unijunction transistor in the oscillator 124. The oscillator 124 is a unijunction relaxation oscillator employing the aforementioned transistor. Varying the emitter resistance to the unijunction transistor changes the frequency of oscillation. The enabling voltage applied to NAND gate 134 through the resistor 196 causes potentiometer 138 to be coupled to the oscillator which is adjusted to given an oscillation frequency that results in the production of ramp signal 2 by the counter and DAC. Likewise, potentiometer139 is adjusted to give an oscillation rate that results in the production of ramp signal 3 which occurs when an enabling voltage is applied to NAND gate 135. The enabling voltage applied to AND gate 133 permits the output of the oscillator to pass to the counter for generating the ramp signals 2 and 3.

Oscillator 124 includes a Schmitt trigger for shaping the waveform of the unijunction oscillator signals. The output is a series of clock pulse signals having a frequency established by the value of the resistance settings of either potentiometer 138 or 139. The pulse signals are applied to AND gate 133 which is in turn capacitively coupled to counter 125. Counter 125 is a conventional eight-bit binary counter which advances positively by a count of one upon receipt of each clock pulse thereby accumulating the number of clock pulses produced by the oscillator. The binary number currently in the counter is constantly applied to DAC 126, of conventional design, which produces a signal having a voltage proportional to the binary number in the counter. The constant rate or frequency of the clock pulses causes the DAC to produce a generally linear ramp signal having a slope related to the constant frequency. The slope of the ramp signal increases and decreases as the frequency of the clock pulses increases and decreases. The slopes of the ramp signal curve are related to the number of bit positions in the counter as well as the frequency of the clock pulses. The output of the DAC 126 is the integral of the clock pulse rate, therefore, if the clock pulse rate is constant the DAC output is a ramp signal and if the clock rate increases linearly the DAC output is an exponential signal. In the present embodiment the clock rate is generally held at a constant level.

Manual switch 140 connects one of the three logic gates 142, 143 and 144 to NAND gate 135. The logic gates are diode gates selected to generate an enabling signal for NAND gate 135 at some predetermined number accumulated by counter 125. The number selected establishes the breakover point 35 on curve 1. That is, the logic gates select the point at which the slope of the ramp signal is changed. The output of NAND gate 135 inhibits gate 134 thereby disabling potentiometer 138 and coupling potentiometer 139 to the oscillator 124. Positive feedback from gate 134 permanently enables NAND gate 135. The coupling of potentiometer 139 to the oscillator lowers the frequency of the clock signals. Consequently, counter 125 accumulates binary counts at a slower but constant rate and the slope of the ramp signal at the output of DAC decreases to correspond with the slope of curve 3 in FIG. 2a. The particular numbers in counter to which the logic gates 142, 143 and 144 are responsive and the particular frequencies of the clock signals are chosen to produce a waveform which best suits the force rate variations required to cold work" a particular size titanium alloy rivet or to perform some other closely controlled squeezing operation.

Quarter count gate 146 is a diode logic gate which produces an output signal at and after the counter 125 registers the binary number representing the pressure amplitude at which a rivet is sufficiently expanded to lock it into the articles being riveted. The output of gate 146 energizes the float relay 172 (FIG. 5) causing the clamp cylinders to float. This opera tion is explained in more detail in connection with the descrip tion of the circuit in FIG. 5.

The maximum count gate 147 is also a diode logic gate and it produces an output signal when the binary number in counter 125 reaches a value representing the maximum pressure level 36 on curve 1. The output from the maximum count gate is fed back to the counter 125 where it inhibits the counter thereby rendering the counter unresponsive to additional clock pulses coming from the oscillator 124. The maximum binary number triggering gate 147 is held by the counter for a period corresponding to the delay period 36a in FIG. 2a. The output from gate 147 is simultaneously applied to timedelay relay 148 (FIG. 6) which initiates the delay period 36a and the subsequent decompression and retraction of the squeeze cylinders 27 and 28. This operation is explained more fully in connection with the description of the circuit in FIG. 6.

The output of the DAC 126 is continuously applied to potentiometer 149 which establishes the voltage range for curve 1 and therefore establishes the maximum pressure level for the squeeze cylinders. The wiper arm 150 of the potentiometer is coupled to amplifier 128. The operational amplifier 128 is a power amplifier which inverts the signal on the wiper arm 150, slews the charging current on capacitor 129 and provides a control voltage to current control circuit 130. The capacitor 129 is charged to the amplitude of the output of amplifier 128. At the end of the delay period 36a (FIG. 2a), the normally closed contacts 157 open and the normally open contacts 156 close thereby converting the operational amplifier 128 to a simple lag rate integrator circuit which produces an exponentially decaying output signal corresponding to the portion 4 of curve 1 in FIG. 2a that is applied to the solenoid 122 by current control 130.

Turning now to FIG. 6, the squeeze cylinders are manually controlled by the pushbuttons 150 and 151. Manual control is provided for only the top squeeze cylinder and the relief valve 103 is inserted into the fluid circuit to limit pressure buildup in the top squeeze cylinder during manual operation. Pushbutton 150 energizes solenoids 20v and 542 for extending the top squeeze cylinder and inserting valve 103 into the fluid circuit whereas pushbutton 151 energizes solenoid 20y for retracting the cylinder 27. Solenoid 49x on the range valve 49 is also energized by pushbutton 150 if the range switch 152. is thrown to the low force range position to close contacts 152a. Curves 29 and 30 in FIG. 2a represent manual jogging of cylinder 27.

The automatic operation of the squeeze cylinders, as discussed earlier, is initiated by closing the start switch 125'. Switch 123 (FIG. 6) applies the +v voltage to the solenoids 20v and 54 to extend the top squeeze cylinder and to insert relief valve 103 into the fluid circuit. (The schematic representations of the valves and solenoids in FIGS. 4, 5 and 6 correspond to that in FIG. 1 and include an internal ground for the solenoids). Solenoid 49): is also energized if the low force range is selected by switch 152 thereby closing contacts 152b. The +v voltage is simultaneously applied to time-delay relay 131 discussed earlier. The normally open contacts 127 of relay 131 close after a time delay corresponding to the duration between the leading edges of curves 31and 32 in FIG. 2a. Contacts 127 apply the +v voltage to solenoid 48w to extend the bottom squeeze cylinders 28 and to energize timedelay relay 132. The contacts 119 and 120 of relay 132 are switched following a time period corresponding to the duration of curve 32 and delay period 33. Contacts 119 open to deenergize solenoid 54z thereby removing the relief valve 103 from the fluid circuit. The opening of contacts 120 removes the ground from the counter 125 and DAC 126 and applies the v voltage to the gates 133 and 134 to begin the generation of the ramp signal 2 of FIG. 2a.

The fluid pressure in the squeeze cylinders increases according to ramp 2 until the breakover point 35 at which time one of the gates 142, 143 and 144, selected by switch 140 (FIG. 3), changes the slope of the increasing fluid pressure to correspond to ramp 3 in FIG. 2a. When the fluid pressure reaches the maximum level 36, maximum count gate 147 inhibits the counter 125 to hold the pressure constant and energizes time-delay relay- 148 to initiate the delay period 360 (FIG. 2a). At the end of the delay period 36a, the normally open contacts 153 of relay 148 close and the normally closed contacts 154 of relay 148 open. Opening contacts 154 removes the +v voltage from relay 132 thereby coupling the ground 1 16 through contacts 120 to the counter 125 and DAC 126 to reset them to zero. The normally closed contacts 155 of relay 148 are also opened at this time to prevent solenoid 54 from being energized. The contacts 156 and 157 of relay 148 coupled to the capacitor 129 and amplifier 128 in FIG. 3 are also switched at the end of delay period 36a to begin decompression of the squeeze cylinders according to portion 4 of curve 1. (Relay 148 is latched through diode 197 as max count gate 147 goes to when the counter 125 is reset).

The decompression of the squeeze cylinders continues for a period determined by time-delay relay 159 (the squeeze decompression timer) which is energized at the end of the delay period 36a throughthe contacts 153 of relay 148. At the end of the decompression period as established by relay 159, the normally closed contacts 160 or relay 159 open to remove the +v voltage from solenoids 20v and 48w. The +v voltage is removed from solenoid 48w because relay 131 has the +v voltage removed from it at this time. The normally open contacts 161 of relay 159 are closed to apply the +v voltage to solenoid 20y thereby retracting the squeeze cylinders. When the fluid pressure in the retraction chambers increases to the level indicated by point 41a in FIG. 2a, the pressure switch 118 is activated opening contacts 162 of the pressure switch to deenergize relay 159. At this time all the relays and solenoids are at their initial states and the master valve 20 is at its center position thereby preventing fluid from being routed to the squeeze cylinders. (This assumes start switch 123 is at its initial open position) The decompression and retraction of squeeze cylinders can be started at any time by the override switch 163 which energizes relay 148 when closed. Energizing relay 148 starts the above-described decompression and retraction of the squeeze cylinders.

The clamp curve in FIG. 1 and the various valves in the clamp fluid circuit are controlled by the circuits in FIGS. 4 and 5. The manual jogging of the clamp cylinders 14 and is controlled by pushbuttons 168, 169 and 170 (FIG. 5). The top clamp cylinders 14 are extended and retracted by buttons 168 and 169 and the bottom clamp cylinders are extended by button 170. Button 168 applies the +v voltage to solenoids 17c and 19a for extending the top clamp cylinders and button 169 applies the +v voltage to solenoids 17g and 19b for retracting the top cylinders 14. Button 168 also energizes solenoid 46:? if the low force range is selected by range switch 152 thereby passing the +v voltage through contacts 152:. Button 170 upplies the +v voltage to solenoids 18d and 19a in order to extend the bottom clamp cylinders 15. Solenoid 47f is also encrgized by button 170 if switch 152 is at the low range position with contacts 152e closed.

The automatic clamp operation begins with closing the contactsof start clamp switch 171. The +v voltage is applied through switch 171 (FIG. 5) to solenoids 17c, 18d and 19a. The +v voltage is also applied to solenoids 46c and 47f if range switch 152 selects the low force range by closing contacts 152d and 152f. The valves 17, 18 and 19 switch to their left valve positions to extend the top and bottom clamp cylinders 14 and 15. The fluid pressure in the extension chambers of the clamp cylinders increases according to the portion 7 of curve 5 (FIG. 2b).

The fluid pressure in the clamp cylinders increases to the level 8 (FIG. 2b) and is held constant. Subsequently, the squeeze operation is begun as described earlier and when the squeeze fluid pressure reaches point 34 on curve 1 (FIG. 2a), the quarter count gate 146 produces an output that floats the clamp cylinders. Gate 146 applies an energizing voltage to the float relay 172 when point 34 is reached on curve 2 as explained earlier. At this time, contacts 173 remove the +v voltage from solenoid 19a and contacts 174 apply the +v voltage to solenoid 19b thereby shifting the float valve 19 to its right valve position. This opens pilot operated valve 45 thereby floating the clamp cylinders.

The fluid pressure in the clamp cylinders remains at the level 8 (FIG. 212) until an operator initiates the decompression and retraction of the cylinders by closing the contacts of stop switch 175 (FIG. 5). However, an interlock circuit prevents the clamp cylinders from being decompressed until the pressure in the squeeze cylinders is reduced to a safe level such as the level of point 37 on curve 1.

The interlock relay 177 (the interlock timer) is a time-delay relay and it is energized upon closing of the normally open contacts 178 of relay 148. Contacts 178 close at the end of the delay period 36a (FIGS. 2a). Contacts 179 on relay 177 close after a time period corresponding to the time period beginning at the end of delay period 3611 and ending at point 37 on curve 1. Once contacts 179 are closed, the closing of the stop clamp switch 175 (FIGS. 4 and 5) initiates the decompression and retraction of the clamp cylinders 14 and 15. Upon closing stop switch 175, time-delay relay 180 (the clamp decompression timer) is energized and the fluid pressure decays according to portion 9 of curve 5 (FIG. 2b). The decompression period is established by relay 180 and continues until the fluid pressure in the clamp cylinders reaches the level 39 (FIG. 2b). At this time, contacts 182 and 183 of relay 180 are switched to their nonnornial positions. Contacts 182 open to remove the +v voltage from solenoids 17c and 18d. (The +v voltage is removed from solenoid 19a at an earlier time by the action of quarter count gate 146.). Contacts 183 close to apply the +v voltage to solenoids 17g and 1811 thereby causing the top and bottom clamp cylinders to retract. (Solenoid 19b is energized at an earlier time by the action of gate 146.) When normally open contacts 181 of relay 180 close, plus voltage is provided through these contacts and normally open contacts 176 of relay 172 to latch relay 172 closed. Thus solenoid 19b continues energized during clamp retraction. Pressure switch 95 is in the fluid circuit of FIG. 1 and is activated when the clamp cylinders are fully retracted and the fluid pressure increases to the level of 42a on curve 5 (FIG. 2b). The normally closed contacts 185 of switch 95 are opened at this time to deenergize relay 180 and therefore the solenoids on master valves 17 13 and 19 (and 46 and 47 if low range is selected). The fluidoperated clamp circuit in FIG. 1 and the electrical circuit of FIG. 5 are thereby returned to their initial state. (This assumes that start switch 171 is open.

FIG. 4 illustrates the circuit used to produce the clamp curve 5 in FIG. 2b. The curve 5 is generated by charging the capacitor 188 toward the voltage level established by potentiometcr 189 to produce the portion 7, by holding the voltage on the capacitor at this level to produce the portion 8 and by discharging the capacitor to produce the portion 9. The voltage on the capacitor establishes like changes in the current control circuit 196) which drives the solenoid on the relief valve 84 in the clamp fluid circuit represented by coil 191. Re lief valve 84 limits the pressure in the extension chambers of the clamp cylinders 14 and 15 to a value corresponding to curve 5 as explained in the description of the hydraulic circuit.

Closing the start clamp switch 171 (the same switch discussed in connection with FIG. 5) applies the +v voltage to potentiometer 189 and the capacitor 188 is charged to a predetermined voltage level represented by level 8 in FIG. 2b. The voltage on the capacitor remains at level 8 until the stop switch 175 (the same switch discussed in connection with FIG. is closed and the interlock timer, relay 177, has expired. Switch 175 (F104) applies a+v voltage to relay 192 provided the normally open contacts 194 of interlock relay 177 have been closed indicating that the squeeze cylinders have decom-.

pressed to level 37 on curve 1. With relay 192 energized, its normally closed contacts 193 open thereby removing the +v voltage from potentiometer 189. The capacitor begins to discharge toward ground and when its voltage reaches a level corresponding to level 39 in FIG. 2b, the clamp decompression timer (relay 180 in FIG. 5) is expired and causes the clamp cylinders to retract. The capacitor continues to discharge to ground without adversely affecting the retraction of the clamp cylinders. At that time, the components of the circuits in FIGS. 4 and 5 are at their initial states or conditions. (Again, this assumes that the start and stop switches in FIGS. 4 and 5 are in their open positions).

The mechanical and/or electrical interlocks for the various switches, particularly start squeeze switch 123 and at the start and stop clamp switches 171 and 175, have not been shown to simplify the description of the invention. Appropriate means are utilized to insure that these manually operated switches are always in their proper switch positions.

The foregoing description of the electrical circuitry has been related to the specific operation cycle and fluid pressure variations represented by curve 1 in FIG. 1. It should be understood, that the circuit of FIG. 3 is capable of producing a variety of curves for the squeeze cycle of a compression tool. By way of example, the slope of the ramp 3 is readily made greater than that of ramp 2 by merely adjusting the poten tiometers 138 and 139. Also, additional potentiometers corresponding to 138 and 139 can be coupled to the oscillator to provide more than one slope change.

It is believed that the invention will have been clearly understood from the foregoing detailed description of my nowpreferred illustrated embodiment. Changes in the details of construction may be resorted to without departing from the spirit of the invention and it is accordingly my intention that no limitations be implied and that the invention be given the broadest interpretation to which the employed language fairly admits.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for continuously controlling the movement and force exerted by a tool throughout a work cycle of the tool comprising a fluid-operated squeeze circuit having means for changing the direction of fluid flow and for varying fluid pressure in response to electrical command signals, fluid-operated squeeze cylinders in fluid communication with said squeeze circuit and operatively coupled to the tool enabling the tool to engage, squeeze and disengage a workpiece during a work cycle in response to the pressure and flow direction of fluid in said squeeze circuit, and an electrical command circuit coupled to said squeeze circuit for establishing the operations of the tool during a work cycle for generating electrical squeeze command and squeeze. decompression signals controlling fluid pressure. in said squeeze circuit, and generating electrical switching command signals changing fluid flow direction in said squeeze circuit effecting engagement, squeezing and disengagement ofa workpiece by the tool. 2. The apparatus of claim 1 wherein said electrical command circuit includes a squeeze cycle generator for producing an electrical squeeze command signal corresponding to fluid pressure variations desired in said fluid-operated squeeze circuit,

output means for coupling said squeeze signal to said means for varying fluid pressure in said squeeze circuit to effect fluid pressure variations proportional to said squeeze command signal, and

gating means coupled to said squeeze cycle generator for producing switching command signals at predetermined times during the generation of said squeeze command signal. 5 3. The apparatus of claim 1 wherein said electrical com mand circuit includes a ramp generator for producing a ramp signal in response to an electrical start signal having predetermined starting and final signal amplitudes,

breakpoint means for varying the slope of said ramp signal at predetermined amplitudes of said ramp signal.

a decompression cycle generator for producing a decaying signal having a maximum amplitude substantially equal to the final amplitude of said ramp signal, and

switching means responsive to the final amplitude of said ramp signal for coupling said ramp signal to said fluid operated squeeze circuit prior to the final signal amplitude and thereafter coupling said decaying signal to said squeeze circuit.

4. The apparatus of claim 1 wherein said electrical command circuit includes a variable oscillator responsive to a start signal for generating clock pulse signals,

a counter coupled to said oscillator for accumulating the number of clock pulses received from said oscillator,

breakpoint means coupled to said counter for varying the frequency of said clock pulses at predetermined numbers accumulated by said counter, and

a digital to analog converter operatively coupled to said counter for generating a signal having an amplitude corresponding to the number of clock pulses accumulated by said counter.

5. The apparatus of claim 4 wherein said breakpoint means includes first logic gates coupled to said counter and oscillator for generating breakpoint signals to change the frequency of said clock pulses at predetermined accumulated counts in said counter.

6. The apparatus of claim 4 further including a maximum count gate coupled to said counter for inhibiting said counter in response to the number accumulated by said counter representing the final amplitude of said ramp signal.

7. The apparatus of claim 6 further including a decompression signal generator coupled to said maximum count gate for producing a decaying signal after said ramp signal has reach its final amplitude and switching means coupled to said maximum count gate for coupling said ramp signal to said fluid operated squeeze circuit prior to said ramp signal reaching its final amplitude and thereafter for coupling said decaying signal to said fluid operated squeeze circuit.

8. The apparatus of claim 1 wherein said fluid operated squeeze circuit includes a squeeze circuit pressure switch in fluid communication with said squeeze cylinders and coupled to said command circuit for detecting the disengagement of said workpiece by said tool to initialize the components in said squeeze and command circuits thereby readying the apparatus for subsequent work cycles.

9. The apparatus of claim 1 wherein said electrical command circuit includes means for generating an electrical clamp command signal and further including top-and-bottom double-acting clamp cylinders for gripping and holding articles associated with a workpiece operated on by said tool having extension and retraction chambers for receiving fluid for extending and retracting said clamp cylinders, and

a fluid-operated clamp circuit electrically coupled to said command circuit and in fluid communication with said clamp cylinders having a pump for delivering fluid to said clamp cylinders, electrically operated master valves for routing fluid to and from the extension and retraction chambers of said clamp cylinders in response to switching command signals, electrically controlled check valve means for floating said clamp cylinders in response to a switching command signal and electrically controlled fluid pressure varying means for controlling the fluid pressure level in the extension chambers of said clamp cylinders in response to said clamp command signal.

10. The apparatus of claim 9 wherein said fluid operated clamp circuit includes a clamp circuit pressure switch in fluid communication with said clamp cylinders and coupled to said command circuit for detecting retraction of said clamp cylinders for releasing their grip on the articles to initialize the components in said clamp and command circuits for subsequent work cycles.

ll. A system for controlling the movement and force exerted by opposed tools comprising top-and-bottom fluid-operated, double-acting squeeze cylinders having pistons therein with piston rods projecting from the cylinders and extension and retraction chambers for receiving fluid to extend and retract said piston rods and said opposed tools coupled thereto,

a fluid pump having control means for varying the fluid pressure at the output of said pump in response to electrical signals,

a solenoid-operated master squeeze valve in fluid communication with said pump and said squeeze cylinders for routing fluid to the squeeze cylinders for extension and retraction of the rods,

an electrical command circuit for generating electrical squeeze command and squeeze decompression signals applied to said pump control means to obtain desired fluid pressure levels within said cylinders,

a relay logic circuit coupled to said command circuit and solenoids on said master valve having start means for ac tivating a. solenoid on said master valve to extend the piston rods of said squeeze cylinders and to initiate generation of said squeeze command signal and having a decompression timer for initiating the generation of said squeeze decompression signal at the end of said squeeze command signal and for activating a solenoid on said master valve to retract the piston rods of squeeze cylinders after decompression of the fluid pressure therein.

12. The system of claim 11 further including a solenoidoperated pressure limit valve in fluid communication with said squeeze cylinders for coupling and removing a relief valve to and from said cylinders and wherein said relay logic circuit includes a pressure limit timer for activating a solenoid on said pressure limit valve to couple said relief valve to said squeeze cylinders during the initial extension thereof, for activating said pressure limit valve solenoid to remove saidrelief valve after initial extension of said piston rods and for inhibiting generation of said squeeze command signal until removal of said relief valve from the squeeze cylinders.

13. The system of claim 12 further including a solenoid operated auxiliary valve in fluid communication with said master valve and said bottom squeeze cylinder for extending the piston rod of said bottom cylinder and wherein said relay logic circuit further includes an auxiliary timer for inhibiting the actuation of a solenoid on said auxiliary valve until after initial extension of the piston rod of said top squeeze cylinder but before removal of said relief valve from said squeeze cylinders.

14. The system of claim 11 wherein said squeeze command signal includes at least two ramp signals with the slope of su bsequent ramp signals different from that of preceding ramp signals and with said rarnp signals increasing in amplitude to a maximum level and wherein said squeeze decompression signal includes a decreasing signal having an initial amplitude substantially equal to said maximum level of said ramp signals.

15. The system of claim 11 further including a solenoid operated range valve in fluid communication with said master valve and said squeeze cylinders for selectively routing fluid to both the extension and retraction chambers of said cylinders during extension thereof, whereby two force ranges for a given fluid pressure range are provided for said cylinders.

16. The system of claim lll further including top-and-bottom fluid-operated, double-acting clamp cylinders having extension and retraction chambers for receiving fluid for extending and retracting the piston rods of said cylinders with said rod gripping and holding articles associated with a workpiece operated on by said squeeze cylinders,

a fluid pump for providing pressurized fluid,

first and second solenoid-operated master clamp valves in fluid communication with the top and bottom clamp cylinders respectively and with said fluid ramp,

electrical fluid pressure control means in fluid communication with the extension chambers of said clamp cylinders for establishing the pressure level therein in response to electrical signals,

a pilot-operated check valve in fluid communication with the extension chamber of the bottom clamp cylinder to limit fluid flow direction there through toward the bottom cylinder extension chamber when said check valve is closed thereby locking the top and bottom cylinders against relative movement and to allow free flow of fluid there through, when open, to float said clamp cylinders, and

a solenoid-operated float valve in fluid communication with said pump and the pilot operator of said pilot operated check valve for opening said check valve in response to an electrical signal applied to a solenoid on said float valve, and

wherein said relay logic circuit further includes clamp start means for activating solenoids on said mater clamp valves to extend said clamp cylinders and for initiating generation of said clamp signal, and

clamp stop means for activating solenoids on said master clamp valves to retract said clamp cylinders, and

wherein said electricai command circuit further includes means for generating an electrical clamp pressure signal and an electrical clamp decompression signal applied to said fluid pressure control means for establishing the fluid pressure in said clamp cylinders, and

means for activating solenoids on said float valve to float said clamp cylinders at a predetermined squeeze signal level, and

interlock means for inhibiting said clamp decompression signal until a predetermined squeeze decompression signal level, and

interlock means for inhibiting said clamp stop means until a predetermined clamp decompression signal level.

17. The system ofclaim 16 further including first bias means coupled to said squeeze cylinders to create a pressure differential between the fluid in the extension chambers of said top and bottom squeeze cylinders creating a net downward force on the tools coupled to said squeeze cylinders, and

second bias means coupled to said clamp cylinders to create a pressure differential between fluid in the extension chambers of said clamp cylinders creating a net upward force on the articles associated with the tools with the tool coupled to said top squeeze cylinder bearing against said articles as well as a workpiece to lock said squeeze cylinders against relative movement prior to floating of said clamp cylinders.

18. The system of claim 16 further including solenoid-operated squeeze range valves in fluid communi cation with said master squeeze valve and said squeeze cylinders for selectively routing fluid to the extension and retraction chambers during extension to provide two force ranges for said squeeze cylinders for a given fluid pressure range, and

solenoid-operated clamp range control valves in fluid communication with said master clamp valves and said clamp cylinders for selectively routing fluid to the extension and retraction chambers during extension to provide two force ranges for said clamp cylinders for a given fluid pressure range.

1?. A method of forming titanium alloys comprising the first forming step of exerting an increasing compression force on the alloy at a first generally linear rate of change of force to a first force level, and

exerting continuing increasing compression forces on the alloy from said first force level to succeeding force levels at subsequent generally linear rates of change of force, up to a maximum force level, and i the second step of exerting a controller-regulated decreasing compression force on the alloy from the maximum force level to a minimum force level. 20. A method of riveting overlapping articles with titanium alloy rivets comprising inserting a titanium alloy rivet through a hole in the overlapped articles, engaging the articles with clamps coupled to top and bottom clamp cylinders and exerting an increasing compression force on the articles to a maximum clamp force level, engaging the rivet with tooling coupled to top and bottom squeeze cylinders and exerting an increasing compression force on the rivet at a first generally linear rate of change of force to a first force level, and

exerting continuing increasing compression forces on the rivet from said first force level to succeeding force levels at subsequent generally linear rates of change of force, up to a maximum squeeze force level,

floating said clamp cylinders, but not changing said clamp force level, upon reaching a predetermined squeeze force level at which the rivet is sufficiently deformed to be locked in position in said hole in the articles,

exerting a controller-regulated decreasing compression force on the rivet from said maximum squeeze force level to a minimum squeeze force level,

exerting a controller-regulated decreasing clamp force on said articles, after a predetermined decreased squeeze force level, from said maximum clamp force level to a minimum clamp force level,

disengaging said squeeze cylinders and tooling from the rivet at the minimum squeeze force level, and

disengaging said clamp cylinders and clamps from the articles at the minimum clamp force level. 

2. The apparatus of claim 1 wherein said electrical command circuit includes a squeeze cycle generator for producing an electrical squeeze command signal corresponding to fluid pressure variations desired in said fluid-operated squeeze circuit, output means for coupling said squeeze signal to said means for varying fluid pressure in said squeeze circuit to effect fluid pressure variations proportional to said squeeze command signal, and gating means coupled to said squeeze cycle generator for producing switching command signals at predetermined times during the generation of said squeeze command signal.
 3. The apparatus of claim 1 wherein said electrical command circuit includes a ramp generator for producing a ramp signal in response to an electrical start signal having predetermined starting and final signal amplitudes, breakpoint means for varying the slope of said ramp signal at predetermined amplitudes of said ramp signal. a decompression cycle generator for producing a decaying signal having a maximum amplitude substantially equal to the final amplitude of said ramp signal, and switching means responsive to the final amplitude of said ramp signal for coupling said ramp signal to said fluid operated squeeze circuit prior to the final signal amplitude and thereafter coupling said decaying signal to said squeeze circuit.
 4. The apparatus of claim 1 wherein said electrical command circuit includes a variable oscillator responsive to a start signal for generating clock pulse signals, a counter coupled to said oscillator for accumulating the number of clock pulses received from said oscillator, breakpoint means coupled to said counter for varying the frequency of said clock pulses at predetermined numbers accumulated by said counter, and a digital to analog converter operatively coupled to said counter for generating a signal having an amplitude corresponding to the number of clock pulses accumulated by said counter.
 5. The apparatus of claim 4 wherein said breakpoint means includes first logic gates coupled to said counter and oscillator for generating breakpoint signals to change the frequency of said clock pulses at predetermined accumulated counts in said counter.
 6. The apparatus of clAim 4 further including a maximum count gate coupled to said counter for inhibiting said counter in response to the number accumulated by said counter representing the final amplitude of said ramp signal.
 7. The apparatus of claim 6 further including a decompression signal generator coupled to said maximum count gate for producing a decaying signal after said ramp signal has reach its final amplitude and switching means coupled to said maximum count gate for coupling said ramp signal to said fluid operated squeeze circuit prior to said ramp signal reaching its final amplitude and thereafter for coupling said decaying signal to said fluid operated squeeze circuit.
 8. The apparatus of claim 1 wherein said fluid operated squeeze circuit includes a squeeze circuit pressure switch in fluid communication with said squeeze cylinders and coupled to said command circuit for detecting the disengagement of said workpiece by said tool to initialize the components in said squeeze and command circuits thereby readying the apparatus for subsequent work cycles.
 9. The apparatus of claim 1 wherein said electrical command circuit includes means for generating an electrical clamp command signal and further including top-and-bottom double-acting clamp cylinders for gripping and holding articles associated with a workpiece operated on by said tool having extension and retraction chambers for receiving fluid for extending and retracting said clamp cylinders, and a fluid-operated clamp circuit electrically coupled to said command circuit and in fluid communication with said clamp cylinders having a pump for delivering fluid to said clamp cylinders, electrically operated master valves for routing fluid to and from the extension and retraction chambers of said clamp cylinders in response to switching command signals, electrically controlled check valve means for floating said clamp cylinders in response to a switching command signal and electrically controlled fluid pressure varying means for controlling the fluid pressure level in the extension chambers of said clamp cylinders in response to said clamp command signal.
 10. The apparatus of claim 9 wherein said fluid operated clamp circuit includes a clamp circuit pressure switch in fluid communication with said clamp cylinders and coupled to said command circuit for detecting retraction of said clamp cylinders for releasing their grip on the articles to initialize the components in said clamp and command circuits for subsequent work cycles.
 11. A system for controlling the movement and force exerted by opposed tools comprising top-and-bottom fluid-operated, double-acting squeeze cylinders having pistons therein with piston rods projecting from the cylinders and extension and retraction chambers for receiving fluid to extend and retract said piston rods and said opposed tools coupled thereto, a fluid pump having control means for varying the fluid pressure at the output of said pump in response to electrical signals, a solenoid-operated master squeeze valve in fluid communication with said pump and said squeeze cylinders for routing fluid to the squeeze cylinders for extension and retraction of the rods, an electrical command circuit for generating electrical squeeze command and squeeze decompression signals applied to said pump control means to obtain desired fluid pressure levels within said cylinders, a relay logic circuit coupled to said command circuit and solenoids on said master valve having start means for activating a solenoid on said master valve to extend the piston rods of said squeeze cylinders and to initiate generation of said squeeze command signal and having a decompression timer for initiating the generation of said squeeze decompression signal at the end of said squeeze command signal and for activating a solenoid on said master valve to retract the piston rods of squeeze cylinders after decompression of the fluid pressure therein.
 12. The system of claim 11 further including a solenoid-operated pressure limit valve in fluid communication with said squeeze cylinders for coupling and removing a relief valve to and from said cylinders and wherein said relay logic circuit includes a pressure limit timer for activating a solenoid on said pressure limit valve to couple said relief valve to said squeeze cylinders during the initial extension thereof, for activating said pressure limit valve solenoid to remove said relief valve after initial extension of said piston rods and for inhibiting generation of said squeeze command signal until removal of said relief valve from the squeeze cylinders.
 13. The system of claim 12 further including a solenoid operated auxiliary valve in fluid communication with said master valve and said bottom squeeze cylinder for extending the piston rod of said bottom cylinder and wherein said relay logic circuit further includes an auxiliary timer for inhibiting the actuation of a solenoid on said auxiliary valve until after initial extension of the piston rod of said top squeeze cylinder but before removal of said relief valve from said squeeze cylinders.
 14. The system of claim 11 wherein said squeeze command signal includes at least two ramp signals with the slope of subsequent ramp signals different from that of preceding ramp signals and with said ramp signals increasing in amplitude to a maximum level and wherein said squeeze decompression signal includes a decreasing signal having an initial amplitude substantially equal to said maximum level of said ramp signals.
 15. The system of claim 11 further including a solenoid operated range valve in fluid communication with said master valve and said squeeze cylinders for selectively routing fluid to both the extension and retraction chambers of said cylinders during extension thereof, whereby two force ranges for a given fluid pressure range are provided for said cylinders.
 16. The system of claim 11 further including top-and-bottom fluid-operated, double-acting clamp cylinders having extension and retraction chambers for receiving fluid for extending and retracting the piston rods of said cylinders with said rod gripping and holding articles associated with a workpiece operated on by said squeeze cylinders, a fluid pump for providing pressurized fluid, first and second solenoid-operated master clamp valves in fluid communication with the top and bottom clamp cylinders respectively and with said fluid ramp, electrical fluid pressure control means in fluid communication with the extension chambers of said clamp cylinders for establishing the pressure level therein in response to electrical signals, a pilot-operated check valve in fluid communication with the extension chamber of the bottom clamp cylinder to limit fluid flow direction there through toward the bottom cylinder extension chamber when said check valve is closed thereby locking the top and bottom cylinders against relative movement and to allow free flow of fluid there through, when open, to float said clamp cylinders, and a solenoid-operated float valve in fluid communication with said pump and the pilot operator of said pilot operated check valve for opening said check valve in response to an electrical signal applied to a solenoid on said float valve, and wherein said relay logic circuit further includes clamp start means for activating solenoids on said mater clamp valves to extend said clamp cylinders and for initiating generation of said clamp signal, and clamp stop means for activating solenoids on said master clamp valves to retract said clamp cylinders, and wherein said electrical command circuit further includes means for generating an electrical clamp pressure signal and an electrical clamp decompression signal applied to said fluid pressure control means for establishing the fluid pressure in said clamp cylinders, and means for activating solenoids on said float valve to float said clamp cylinders at a predetermined squeeze signal level, and interlock means for inhibiting said clamp decompression signal until a predetermined squeeze decompression signal level, and interlock means for inhibiting said clamp stop means until a predetermined clamp decompression signal level.
 17. The system of claim 16 further including first bias means coupled to said squeeze cylinders to create a pressure differential between the fluid in the extension chambers of said top and bottom squeeze cylinders creating a net downward force on the tools coupled to said squeeze cylinders, and second bias means coupled to said clamp cylinders to create a pressure differential between fluid in the extension chambers of said clamp cylinders creating a net upward force on the articles associated with the tools with the tool coupled to said top squeeze cylinder bearing against said articles as well as a workpiece to lock said squeeze cylinders against relative movement prior to floating of said clamp cylinders.
 18. The system of claim 16 further including solenoid-operated squeeze range valves in fluid communication with said master squeeze valve and said squeeze cylinders for selectively routing fluid to the extension and retraction chambers during extension to provide two force ranges for said squeeze cylinders for a given fluid pressure range, and solenoid-operated clamp range control valves in fluid communication with said master clamp valves and said clamp cylinders for selectively routing fluid to the extension and retraction chambers during extension to provide two force ranges for said clamp cylinders for a given fluid pressure range.
 19. A method of forming titanium alloys comprising the first forming step of exerting an increasing compression force on the alloy at a first generally linear rate of change of force to a first force level, and exerting continuing increasing compression forces on the alloy from said first force level to succeeding force levels at subsequent generally linear rates of change of force, up to a maximum force level, and the second step of exerting a controller-regulated decreasing compression force on the alloy from the maximum force level to a minimum force level.
 20. A method of riveting overlapping articles with titanium alloy rivets comprising inserting a titanium alloy rivet through a hole in the overlapped articles, engaging the articles with clamps coupled to top and bottom clamp cylinders and exerting an increasing compression force on the articles to a maximum clamp force level, engaging the rivet with tooling coupled to top and bottom squeeze cylinders and exerting an increasing compression force on the rivet at a first generally linear rate of change of force to a first force level, and exerting continuing increasing compression forces on the rivet from said first force level to succeeding force levels at subsequent generally linear rates of change of force, up to a maximum squeeze force level, floating said clamp cylinders, but not changing said clamp force level, upon reaching a predetermined squeeze force level at which the rivet is sufficiently deformed to be locked in position in said hole in the articles, exerting a controller-regulated decreasing compression force on the rivet from said maximum squeeze force level to a minimum squeeze force level, exerting a controller-regulated decreasing clamp force on said articles, after a predetermined decreased squeeze force level, from said maximum clamp force level to a minimum clamp force level, disengaging said squeeze cylinders and tooling from the rivet at the minimum squeeze force level, and disengaging said clamp cylinders and clamps from the articles at the minimum clamp force level. 